Machines for cutting hard surfaces such as used in the trenching and mining industries and for highway cold planning to remove the upper surface of concrete and asphalt pavement, employ tools fitted into tool holders on a rotatable wheel or drum. The tools have a tapered forward cutting end and axially behind the cutting end is a cylindrical shank that rotatably fits within a complementarily shaped bore in the tool holder. Such rotatable tools have an annular rearwardly directed flange between the forward cutting end and the shank that contacts the forward surface of the tool holder. The shank is retained in the bore of the tool holder by a sleeve made of spring steel so as to be compressible and has an unstressed diameter greater than that of the bore, such that compression of the sleeve retains the sleeve within the bore of the tool holder. To prevent the withdrawal of the tool from the tool holder, the sleeve has one or more inwardly directed projections in the inner surface that engage an annular shoulder around the circumference of the shank of the tool.
To maximize the useful life of such tools, the tools are adapted to rotate around the axis of the shank thereby causing the tool to wear evenly about its circumference. A tool in a machine may undergo 50,000 rotations or more during a single work day, and the rotation of the rearwardly directed flange against the forward surface of the tool holder will over time cause the forward surface of the tool holder to become worn away. To prevent such wear, it is common to provide an annular wear ring around the shank of the tool between the forward surface of the tool holder and the rearwardly directed flange of the tool.
Ojanen U.S. Pat. No. 6,478,383 B1 discloses a rotatable cutting tool having a tapered forward end with a rearwardly facing annular flange and a rearwardly extending shank that fits into a tool holder and a wear ring positioned on the shank of the tool behind the radial flange and against the forward surface of the tool holder. The wear ring of Ojanen has a circular outer circumference with a diameter that is less than the diameter of the radial flange of the tool and less than the diameter of the forward surface of the tool holder such that a gap exists between the rearward surface of the flange and the forward surface of the tool holder. Ojanen suggests that the portion of the radial flange that overhangs beyond the diameter of the wear ring can be used to receive an extraction tool for removing the rotatable tool from the tool holder. The tool assembly disclosed by the Ojanen patent, however, has certain disadvantages. First, the Ojanen wear ring is not locked against rotation with the tool and consequently the wear ring rotates, at least to some degree, with the tool. As the wear ring rotates against the forward surface of the tool holder it wears away the portion of the forward surface of the tool holder behind the wear ring. The tools of such machines are frequently replaced because they become rapidly worn, and as the machine is used, the wear from the rotating wear rings create a countersink that becomes deeper with each replaced tool. Eventually, the countersink in the forward surface of the tool holder becomes deep enough that the rearward surface of the flange of the tool will make contact with the forward surface of the tool holder thereby defeating the primary purpose for installing the wear ring. The secondary purpose of the Ojanen wear ring is to facilitate the removal of the tool and that purpose is also defeated as the rearward surface of the wear ring wears away the forward surface of the tool holder because the gap between the rearward surface of the radial flange and the forward surface of the tool holder is gradually reduced.
Briske U.S. Pat. No. 5,931,542 discloses a rotatable tool having a tapered forward cutting end and a cylindrical rearwardly extending shank that is received in a cylindrical aperture of a tool holder and a wear ring between the rearward flange of the tool and the forward surface of the tool holder with the wear ring locked against rotation with the tool. The outer shape of the wear ring is circular and the outer diameter of the wear ring is approximately equal to the diameter of the radial flange of the tool and approximately the same diameter of the forward surface of the tool holder. The wear ring of Briske, therefore, does not aid in the removal of the tool from the tool holder.
I have found that a circular wear ring having a diameter less than the outer dimensions of the forward surface of the tool holder will fail to perform its intended function even where the wear ring is locked against rotation with the tool. To cut hard surfaces, such tools require that a great amount of force be applied from the forward surface of the tool holder against the rear flange of the tool. All the force applied by the cutting tool is therefore applied through the wear ring. Where the wear ring has a small diameter circular periphery, the forward surface of the tool holder becomes indented under the wear ring even though the wear ring is locked against rotation. Over a period of time, the forward end of the tool holder becomes more deeply indented thereby gradually eliminating the gap between the rearward flange of the tool and the forward surface of the tool holder. Eventually, the gap is insufficient to receive an extraction tool for removing the rotatable tool from the tool holder. Ultimately, the indentation becomes so severe that the rearward surface of the radial flange contacts the forward surface of the tool holder and the purpose of the wear ring is again defeated.
To operate properly, the wear ring must remain stationary against the forward surface of the tool holder while the tool rotates. A tool holder that receives tools with wear rings that do not rotate will have four times the useful life of a tool holder receiving tools with wear rings that are not locked against rotation with the tool. Of course, over time, even a tool holder with a non-rotating wear ring must be replaced because the tool rotates within the tool holder and, along with rotating, the tool is subjected to heavy forces. Gradually, the forward surface of the tool holder becomes worn and the retaining bore of the holder enlarges in diameter. Replacement eventually becomes necessary.
In my co-pending application filed Sep. 28, 2004 and issued Ser. No. 10/952,158, I disclose a wear ring having an inwardly directed projection on the inner opening thereof that will engage portions of the upper end of the compressible sleeve to prevent the wear ring from rotating with respect to the tool holder while the tool is in use. In the same application I disclose that an enlarged diameter of the wear ring can be used to facilitate the extraction of the tool from the tool holder. There are circumstances, however, when it is not desirable to have a wear ring, the outer diameter of which is larger than the diameter of the radial flange of the tool. In such circumstances, it is desirable to provide an alternative method of extracting the tool from the tool holder.